HDI(High Density Interconnect board) is a compact circuit board designed for small volume users. Compared with ordinary pcb, the most significant feature of HDI is the high wiring density, and the difference between the two is mainly reflected in the following four aspects.
1.HDI is smaller and lighter
HDI board is a traditional dual panel as the core board, through continuous stacking layer by layer. This kind of circuit board made by continuous layering is also called Build-up Multilayer (BUM). Compared with traditional circuit boards, HDI circuit boards have the advantages of “light, thin, short and small”.
The electrical interconnection between the HDI board is realized through the conductive through hole, buried hole and blind hole connection, its structure is different from the common multi-layer circuit board, and a large number of micro-buried blind holes are used in HDI board. HDI uses direct laser drilling, while standard PCBS usually use mechanical drilling, so the number of layers and aspect ratio tend to be reduced.
2, HDI motherboard production process
The high density of HDI board is mainly reflected in the hole, line, pad density, and layer thickness.
● Micro-pilot hole: HDI board contains micro-pilot hole design such as blind holes, which is mainly displayed in the micro-pore formation technology with aperture less than 150um and the high requirements of cost, production efficiency and hole position precision control. In the traditional multilayer circuit board, there are only through holes and no tiny buried blind holes
● Line width and line distance refinement: its main performance in wire defects and wire surface roughness requirements are more and more stringent. Generally, the line width and line distance do not exceed 76.2um
● High pad density: the welding contact density is greater than 50 per square centimeter
● Thin shape of the medium thickness: it is mainly manifested in the trend of the thickness of the interlayer medium to 80um and below, and the thickness uniformity requirements are becoming more and more stringent, especially for high-density plates and packaging substrates with characteristic impedance control
3, HDI board electrical performance is better
HDI not only enables end-product designs to be miniaturized, but also to meet higher standards of electronic performance and efficiency at the same time.
The increased interconnect density of HDI allows for increased signal strength and improved reliability. In addition, the HDI board has better improvement for RF interference, electromagnetic wave interference, electrostatic discharge, heat conduction and so on. HDI also uses full digital signal process control (DSP) technology and a number of patented technologies, with a full range of load adaptability and strong short-term overload capability.
4.The HDI board has very high requirements for buried holes
It can be seen from the above that whether it is the volume of the board, or the electrical performance, HDI is better than ordinary PCB. Where the coin has two sides, the other side of HDI is as a high-end PCB manufacturing, its manufacturing threshold and process difficulty are much higher than ordinary PCB, and there are more problems to pay attention to when producing – especially the buried hole jack.
At present, the core pain point and difficulty of HDI manufacturing is the buried hole jack. If the HDI hole plug hole is not done well, there will be major quality problems, including uneven edge bumps, uneven media thickness, and potholes in the pad.
● The surface of the board is not smooth, and the line is not straight in the depression to cause the beach phenomenon, which will cause the line gap, broken line and other defects
● The characteristic impedance will also fluctuate due to the uneven dielectric thickness, resulting in signal instability
● The uneven pad makes the subsequent package quality poor resulting in the joint loss of components
Therefore, not all board factories have the ability and strength to do HDI, and QFPCB has been working hard for 16 years. Today, HDI has its own complete system, the whole process is not exported, invested heavily in purchasing advanced equipment, all quality acceptance standards have been adopted IPC2 standards, such as hole copper thickness ≧20μm, to ensure high reliability.
